Method for demodulating UWB pulse sequences

ABSTRACT

The present invention relates to a method for transmitting data in the form of at least one pulse sequence Tsgk (for k=1 to K). The method according to the invention includes at least one symbol decoding step in the course of which at least one modulation value Pwk representative of an amount of power carried by each pulse sequence Tsgk is computed and compared to at least one predetermined threshold value thk 1 , thk 2 . . .  thkM(k). The method according to the invention enables to limit the processing time and power needed for performing the demodulation of a power-modulated UWB signal, since the information carried by such a signal may be recovered by a receiver without said receiver having to map precisely, with respect to time, the received pulse sequences.

BACKGROUND OF THE INVENTION

The present invention relates to a method for transmitting data in atelecommunication system including at least one transmitter and onereceiver, said transmitter being intended to transmit a signal formed byat least one sequence of Ns pulses over Ns time windows, each pulsebeing enclosed within a time chip whose position within its relevanttime window is defined by a chip number.

Such data transmission methods are currently studied with the aim ofassessing the relevance of so-called Ultra-Wide Band telecommunicationsystems (further referred to as UWB systems). In such a system eachtransmitter may be identified by a signature formed by theabove-mentioned chip numbers, which signature is in itself quite sturdyand may thus be reliably and accurately communicated to all potentialreceivers.

The pulses used in UWB systems are very short, having for example aduration lower than 0.1 nanosecond, which offers to such systemsbandwidths at least as large as 10 GigaHertz, entailing high flexibilityand hence numerous possible applications for such systems.

BRIEF SUMMARY OF THE INVENTION

The above-described signal may form a carrying signal on whichinformation can be encoded by modulation of said carrying signal. Theinventors have observed that, because of the shortness of the pulsesinvolved, a precise synchronization with a given pulse sequence will bedifficult to perform at the receiver end, so that the chosen modulationscheme should involve as few time-related parameters as possible inorder to be cost-efficient.

The present invention thus aims at providing a modulation/demodulationscheme according to which the information carried by pulse sequences maybe recovered at the receiver end without said receiver having to mapprecisely, with respect to time, the received pulse sequences.

Indeed, a method for transmitting data as described in the openingparagraph is characterized according to the invention in that itincludes at least one symbol decoding step to be executed at thereceiver end, in the course of which symbol decoding step at least onemodulation value representative of an amount of power carried by eachpulse sequence is computed and compared to at least one predeterminedthreshold value.

The symbol decoding step according to the invention enables to achieve ademodulation of a modulated UWB symbol in a very straightforward manner,by quantifying the power of the received signal and performing simplecomparisons with one or several threshold values, which comparisons areeasy to implement. Such a demodulation scheme does not require thereceiver to perform a precise mapping, with respect to time, of thereceived signal, which in turn enables to manufacture adapted receiversat a relatively low cost.

The modulation of the UWB signals to be demodulated by carrying out sucha symbol decoding step may result from various modulation schemes.

According to a particular embodiment of the invention, a method asdescribed hereinbefore further includes at least one symbol encodingstep to be executed before transmission of said pulse sequence, in thecourse of which symbol encoding step each pulse sequence is multipliedby an integer value representative of a symbol to be carried by saidpulse sequence.

By virtue of this modulation scheme, the information carried by signalstransmitted in Ultra-Wide Band telecommunication systems according tothe invention will essentially be related to the power carried by thesesignals, which power is related to the amplitude of the pulses includedwithin such a signal. Such a modulation scheme is easy to implement,which in turn enables to manufacture adapted transmitters at arelatively low cost.

According to a variant of the invention, each signal to be transmittedis constituted by a superimposition of a predetermined number of pulsesequences, each pulse sequence having been subjected to a symbolencoding step and corresponding to one of several sub-bands into which atotal bandwidth available for transmission has previously been divided.

This variant of the invention enables to transmit simultaneously severalsymbols through a same communication channel, and thus to significantlyincrease the throughput of a telecommunication system in which such avariant of the invention is embodied.

According to one of its hardware-oriented aspects, the invention alsorelates to a telecommunication system including at least one transmitterand one receiver, said transmitter being intended to transmit a signalformed by at least one pulse sequence of Ns pulses over Ns time windows,each pulse being enclosed within a time chip whose position within itsrelevant time window is defined by a chip number, system in which thereceiver includes symbol decoding means intended to compute at least onemodulation value representative of an amount of power carried by eachpulse sequence and to compare said modulation value to at least onepredetermined threshold value.

According to a particular embodiment of this hardware-related aspect,the transmitter includes symbol encoding means intended to multiply eachpulse sequence by an integer value representative of a symbol to becarried by said pulse sequence.

According to a variant of this hardware-related aspect, the transmitterfurther includes signal combination means intended to receive apredetermined number of pulse sequences, each pulse sequence having beengenerated by symbol encoding means and corresponding to one of severalsub-bands into which a total bandwidth available for transmission haspreviously been divided, said signal combination means being intended tocombine all said pulse sequences into a signal to be transmitted.

According to another of its hardware-oriented aspects, the inventionalso relates to a device intended to receive a signal formed by at leastone sequence of Ns pulses over Ns time windows, each pulse beingenclosed within a time chip whose position within its relevant timewindow is defined by a chip number, which receiver includes symboldecoding means intended to compute at least one modulation valuerepresentative of an amount of power carried by each pulse sequence andto compare said modulation value to at least one predetermined thresholdvalue.

According to yet another of its hardware-oriented aspects, the inventionalso relates to a device intended to transmit a signal formed by atleast one sequence of Ns pulses over Ns time windows, each pulse beingenclosed within a time chip whose position within its relevant timewindow is defined by a chip number, which transmitter includes symbolencoding means intended to multiply each pulse sequence by an integervalue representative of a symbol to be carried by said pulse sequence.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The characteristics of the invention mentioned above, as well as others,will emerge more clearly from a reading of the following descriptiongiven in relation to the accompanying figures, amongst which:

FIG. 1 is a functional diagram depicting a telecommunication system inwhich the invention is used;

FIG. 2 is a chronogram depicting a pulse sequence constituting acarrying signal transmitted in such a telecommunication system;

FIG. 3 is a chronogram depicting a pulse model which may be used forgenerating such a sequence;

FIG. 4 is a chronogram depicting a data frame including a plurality ofpulse sequences; and

FIG. 5 is a block diagram depicting symbol decoding means included in areceiver in which a variant of the invention is embodied.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 depicts a telecommunication system SYST in which the presentinvention is embodied. This system SYST includes at least onetransmitter TRD and one receiver RCD, which may for example be bothconstituted by devices such as mobile phones. The transmitter TRD isintended to transmit a signal Tsg formed by at lest one sequence of Nspulses pj (for j=1 to Ns) over Ns time windows, each pulse beingenclosed within a time chip whose position within its relevant timewindow is defined by a chip number cj (for j=1 to Ns). The number Ns ofpulses included in this sequence may, for example, be chosen equal to128, while the width of each time window may be chosen equal to 100nanoseconds, with a width of 1 nanosecond for each time chip.

According to the present invention, the transmitter TRD includes symbolencoding means ENC intended to multiply each pulse sequence by aninteger value representative of a symbol to be carried by said pulsesequence.

The information carried by the transmitted signal Tsg will thusessentially be related to the power carried by this signal Tsg, whichpower is related to the amplitude of the pulses included within saidsignal Tsg. This information may then be recovered by the receiver RCDwithout said receiver RCD having to map precisely, with respect to time,the received pulse sequences.

To this end, the receiver RCD includes symbol decoding means DECintended to compute at least one modulation value representative of anamount of power carried by each pulse sequence and to compare saidmodulation value to at least one predetermined threshold value. As willbe explained hereinafter, the result of such a comparison willautomatically point to the demodulated value of the symbol originallyencoded within the transmitted signal Tsg by the symbol encoding meansENC.

FIG. 2 depicts such a transmitted signal Tsg in the form of achronogram, according to which each pulse sequence has a total durationduration Ts divided into time windows having each a duration Tf, eachtime window being sub-divided into time chips Tc, a single time chipwithin each window being intended to enclose a pulse pj (for j=1 to Ns),which single time chip is identified by means of a chip number cj. Thetransmitter of this transmitted signal Tsg will thus be identified by asignature Sg=(c1, c2 . . . cNs) jointly formed by all above-mentionedchip numbers cj (for j=1 to Ns), which signature Sg is in itself quitesturdy and may thus be reliably and accurately communicated to allpotential receivers.

In accordance with the invention, each pulse pj (for j=1 to Ns)belonging to the pulse sequence shown in this picture has beenmultiplied by a same integer value Vi representative of a symbol to becarried by said pulse sequence, in the form of the power carried by thissequence, the reference “i” being indicative of a reference numberallocated to the pulse sequence under consideration.

Furthermore, the pulses pj (for j=1 to Ns) are multiplied by values (jwhich are randomly chosen equal to +1 or −1 in the course of the symbolencoding step, so that in the example shown here, the second pulse p2 isnegative.

Such a random distribution of positive and negative pulses, which doesnot affect the information carried by said pulses because saidinformation is related to a square form of said pulses, allows toprevent appearance of high-amplitude peaks in the spectral domain, whichpeaks could interfere with equipment not included in thetelecommunication system. Such frequency interference should be limitedas a rule, and is targeted by a European Commission Directive 83/336CEE, as well as by regulation of the USA's Federal CommunicationsCommission.

All pulses pj (for j=1 to Ns) of the pulse sequence shown here mayadditionally be submitted to a time jitter dti in the course of thesymbol encoding step.

This time-jitter, introduced by time-delaying means, will be kept smallwith respect to a delay spread induced by a communication channelthrough which the modulated signal will be transmitted. The delay spreadmay have, for example, a value of 100 nanoseconds. Such a time-jitterwon't affect the information carried by each pulse sequence, and mainlyadds an optional degree of flexibility to the modulation schemeaccording to the invention.

The transmitted signal Tsg may thus be expressed in the following form:

${{Tsg}(t)} = {\sum\limits_{i,j}{{{Vi} \cdot \alpha}\;{j \cdot {{pj}\left( {t - {cj} - {j \cdot {Tf}} - {dti}} \right)}}}}$

FIG. 3 is another chronogram which depicts a possible shape p(t) whichmay be chosen for constituting the above-mentioned pulses. Pulses pj(t)(for j=1 to Ns) of a same sequence may have different shapes, providedthat they all have essentially a same width and carry a same quantity ofenergy. All pulses pj(t) (for j=1 to Ns) belonging to a same sequencemay, however, have a same shape such as the shape p(t) depicted here,which is defined as a derivative of the second order of a Gaussianfunction, which may be expressed mathematically asp(t)=A.[1−4π(t/Tw)²].exp(−2π(t/Tw)²). Other pulse shapes known to thoseskilled in the art may, of course, be used in this same purpose.

Fig. 4 is yet another chronogram which depicts a dataframe DF formed bysuccessive pulse sequences such as the one described above, each havinga total duration Ts, a guard interval GI being periodically insertedbetween two such sequences in order to prevent alteration of a givensequence by a following one, which alterations could be caused, forexample, by intermodulation products between said pulse sequences. Thisdataframe DF is thus constituted by successive frames having each aduration Tr, with Tr=Ts+GI, and including each a pulse sequence asdescribed above.

A device intended to receive such a data frame DF must thus only be ableto measure quantities representative of the successive amounts of powercarried by the successive pulse sequences in order to identify theinformational content of the dataframe DF, without having to mapprecisely, with respect to time, the received pulse sequences.

FIG. 5 depicts symbol decoding means DEC included in a receiveraccording to an alternative embodiment of the invention, in whichembodiment the transmitted signal Tsg is a composite signal including acombination of K pulse sequences as described hereinbefore, each pulsesequence having thus been subjected to a symbol encoding step at thetransmitting end. This receiver includes an antenna device ANT intendedto receive such a composite signal Tsg. The decoding means DEC includean array of K band-pass filters PBFk (for k=1 to K) intended to separatefrom each other K sub-bands into which a total bandwidth used fortransmitting the composite signal Tsg has been divided in order todefine K different pulse sequences intended each to carry a specificsymbol.

This variant of the invention enables to transmit simultaneously severalsymbols through a same communication channel, and thus to significantlyincrease the throughput of a telecommunication system in which such avariant of the invention is embodied.

In such an embodiment, each pulse sequence corresponding to a givensub-band of rank k (with k=1 to K) will be expressed as:

${{{Tsgk}(t)} = {\sum\limits_{i,j}{{{Vki} \cdot \alpha}\;{{kj} \cdot {{pkj}\left( {t - {ckj} - {j \cdot {Tf}} - {dtki}} \right)}}}}},{with}$${{Tsg}(t)} = {\sum\limits_{k}{{Tsgk}(t)}}$

In the embodiment of the invention depicted here, the symbol decodingmeans DEC include an array of K squaring modules SQMk (with k=1 to K),each of which being connected to one of the band-pass filters BPFk andintended to receive a pulse sequence Tsgk (with k=1 to K) and to delivera signal Sqsk constituted by a square of said signal Tsgk.

The symbol decoding means DEC further include an array of K integratingmodules INTk (with k=1 to K), each of which being connected to one ofthe squaring modules SQMk and intended to deliver a modulation value Pwkrepresentative of an amount of power carried by the corresponding pulsesequence Tsgk. Such a modulation value Pwk may for example be computedas the integral, on the duration of the channel delay, of the squaresignal Sqsk delivered by the related squaring module SQMk.

The symbol decoding means DEC also include an array of K comparingmodules CMPMk (with k=1 to K), each of which being connected to one ofthe integrating modules INTk and intended to compare the modulationvalue Pwk to be delivered by said integrating module INTk with a numberM(k) of predetermined threshold values thk1, thk2 . . . thkM(k), whichnumber M(k) may be different from one comparing module to another.

The symbol carried by a given pulse sequence Tsk will thus be identifiedin a very straightforward manner, according to a simple decoding gridwhich may be expressed as follows:

-   -   If Pwk<thk1, then the symbol carried by pulse sequence Tsk is        S0;    -   If thkn<Pwk<thkn+1, then the symbol carried by pulse sequence        Tsk is Sn, for n=1 to M(k)−1; and    -   If thkM(k)<Pwk, then the symbol carried by pulse sequence Tsk is        SM(k).

Various methods may be used by those skilled in the art for defining andcomputing the. Such threshold values may for example be defined byconsidering a linear progression of said values over a whole variationrange of the power which could be carried by received signals, saidrange being then divided into intervals having all essentially a samesize and corresponding each to a given encodable symbol.

However, the definition of the predetermined threshold values thk1, thk2. . . thkM(k) should preferably take into account a non-linearprocessing to be performed in the course of the symbol decoding step,which will involve specific statistical models of unquantifiableparameters such as thermal noise, interference cause by othertransceivers, etc.

Each squaring module SQMk may be formed by a Gilbert cell fed withidentical input signals. Each integrating module INTk may be formed byan operational amplifier provided with an RC feedback. Each comparingmodule CMPMk may be formed by an array of M(k) operational amplifiersintended each to receive a same modulation value Pwk and one of thepredetermined threshold values thk1, thk2 . . . thkM(k) assigned to thiscomparing module CMPMk. The symbol decoding means DEC may thus be formedby off-the-shelf analog circuits, which analog circuits are known fortheir high processing speed and do not require any sampling, as opposedto digital solutions, which will enable to further reduce the processingpower and the time required for performing a signal decoding stepaccording to this embodiment of the invention.

1. A method for transmitting data in a telecommunication systemincluding at least one transmitter and one receiver, the methodcomprising: transmitting, by the transmitter, a signal including a pulsesequence of Ns pulses over Ns time windows, each of the Ns pulses beingenclosed within a time chip whose position within a corresponding timewindow is defined by a chip number and being multiplied by a sameinteger value representative of a symbol to be carried by said pulsesequence; computing a modulation value representative of an amount ofpower related to an amplitude of each of the Ns pulses in the pulsesequence to decode the symbol in the signal; and decoding the symbol inthe signal based on a comparison of the modulation value to at least onepredetermined threshold value, wherein each signal to be transmitted isconstituted by a superimposition of a predetermined number of pulsesequences, each pulse sequence having been multiplied by an integervalue representative of a symbol to be carried by the respective pulsesequence and corresponding to one of several sub-bands into which atotal bandwidth available for transmission has previously been divided.2. The method as claimed in claim 1, further comprising: multiplying,before the transmitting, each of the Ns pulses in the pulse sequence bythe same integer value representative of the symbol to be carried bysaid pulse sequence.
 3. A telecommunication system, comprising: atransmitter configured to transmit a signal including a pulse sequenceof Ns pulses over Ns time windows, each of the Ns pulses being enclosedwithin a time chip whose position within a corresponding time window isdefined by a chip number and being multiplied by a same integer valuerepresentative of a symbol to be carried by said pulse sequence; and areceiver including symbol decoding means for computing a modulationvalue representative of an amount of power related to an amplitude ofeach of the Ns pulses in the pulse sequence to decode the symbol in thesignal, and for decoding the symbol in the signal based on a comparisonof said modulation value to at least one predetermined threshold value,wherein the transmitter further includes signal combination means forreceiving a predetermined number of pulse sequences, each pulse sequencehaving been multiplied by an integer value representative of a symbol tobe carried by the respective pulse sequence and corresponding to one ofseveral sub-bands into which a total bandwidth available fortransmission has previously been divided, said signal combination meanscombining all said pulse sequences into a signal to be transmitted. 4.The telecommunication system as claimed in claim 3, wherein thetransmitter includes symbol encoding means for multiplying each of theNs pulses in the pulse sequence by the same integer value representativeof the symbol to be carried by said pulse sequence.
 5. A receiver,comprising: receiving means for receiving a signal including a sequenceof Ns pulses over Ns time windows, each of the Ns pulses being enclosedwithin a time chip whose position within a corresponding time window isdefined by a chip number and being multiplied by a same integer valuerepresentative of a symbol to be carried by said pulse sequence; andsymbol decoding means for computing a modulation value representative ofan amount of power related to an amplitude of each of the Ns pulses inthe pulse sequence to decode the symbol in the signal, and for decodingthe symbol in the signal based on a comparison of said modulation valueto at least one predetermined threshold value, wherein the receivedsignal is constituted by a superimposition of a predetermined number ofpulse sequences, each pulse sequence having been multiplied by aninteger value representative of a symbol to be carried by the respectivepulse sequence and corresponding to one of several sub-bands into whicha total bandwidth available for transmission has previously beendivided.
 6. A device for transmitting a signal including a sequence ofNs pulses over Ns time windows, each of the Ns pulses being enclosedwithin a time chip whose position within a corresponding time window isdefined by a chip number, comprising: symbol encoding means formultiplying each of the Ns pulses in the pulse sequence by a sameinteger value representative of a symbol to be carried by said pulsesequence, said pulse sequence having an amount of power that is relatedto an amplitude of each of the Ns pulses in said pulse sequence and thatrepresents the symbol to be carried by said pulse sequence; and signalcombination means for receiving a predetermined number of pulsesequences, each pulse sequence having been multiplied by an integervalue representative of a symbol to be carried by the respective pulsesequence and corresponding to one of several sub-bands into which atotal bandwidth available for transmission has previously been divided,said signal combination means combining all said pulse sequences into asignal to be transmitted.
 7. The method as claimed in claim 1, furthercomprising: decoding the symbol carried by the pulse sequence based onthe comparison and a decoding grid that includes at least one symbol topredetermined threshold relationship.
 8. The system as claimed in claim3, wherein the symbol decoding means decodes the symbol carried by thepulse sequence based on the comparison and a decoding grid that includesat least one symbol to predetermined threshold relationship.
 9. Thedevice as claimed in claim 5, wherein the symbol decoding means decodesthe symbol carried by the pulse sequence based on the comparison and adecoding grid that includes at least one symbol to predeterminedthreshold relationship.
 10. A telecommunication system, comprising: atransmitter configured to transmit a signal including a pulse sequenceof Ns pulses over Ns time windows, each of the Ns pulses being enclosedwithin a time chip whose position within a corresponding time window isdefined by a chip number and being multiplied by a same integer valuerepresentative of a symbol to be carried by said pulse sequence; and areceiver including a symbol decoding unit configured to compute amodulation value representative of an amount of power related to anamplitude of each of the Ns pulses in the pulse sequence to decode thesymbol in the signal, and to decode the symbol in the signal based on acomparison of said modulation value to at least one predeterminedthreshold value, wherein the transmitter further includes a signalcombination unit configured to receive a predetermined number of pulsesequences, each pulse sequence having been multiplied by an integervalue representative of a symbol to be carried by the respective pulsesequence and corresponding to one of several sub-bands into which atotal bandwidth available for transmission has previously been divided,said signal combination unit being configured to combine all said pulsesequences into a signal to be transmitted.
 11. A receiver, comprising: areceiving unit configured to receive a signal including a sequence of Nspulses over Ns time windows, each of the Ns pulses being enclosed withina time chip whose position within a corresponding time window is definedby a chip number and being multiplied by a same integer valuerepresentative of a symbol to be carried by said pulse sequence; and asymbol decoding unit configured to compute a modulation valuerepresentative of an amount of power related to an amplitude of each ofthe Ns pulses in the pulse sequence to decode the symbol in the signal,and to decode the symbol in the signal based on a comparison of saidmodulation value to at least one predetermined threshold value, whereinthe received signal is constituted by a superimposition of apredetermined number of pulse sequences, each pulse sequence having beenmultiplied by an integer value representative of a symbol to be carriedby the respective pulse sequence and corresponding to one of severalsub-bands into which a total bandwidth available for transmission haspreviously been divided.
 12. A device for transmitting a signalincluding a sequence of Ns pulses over Ns time windows, each of the Nspulses being enclosed within a time chip whose position within acorresponding time window is defined by a chip number, comprising: asymbol encoding unit configured to multiply each of the Ns pulses in thepulse sequence by a same integer value representative of a symbol to becarried by said pulse sequence, said pulse sequence having an amount ofpower that is related to an amplitude of each of the Ns pulses in saidpulse sequence and that represents the symbol to be carried by saidpulse sequence; and a signal combination unit configured to receive apredetermined number of pulse sequences, each pulse sequence having beenmultiplied by an integer value representative of a symbol to be carriedby the respective pulse sequence and corresponding to one of severalsub-bands into which a total bandwidth available for transmission haspreviously been divided, said signal combination unit being configuredto combine all said pulse sequences into a signal to be transmitted.